Power supply is the basic equipment to provide operation 10 power to computer systems. As applications of the Internet and multimedia technology become more advanced, demand for reliable power supply also grows. Hence how to prevent the power supply from being damaged in the condition of heavy workload or overload in a long period of time, and avoid the computer system from operation interruption or damage due to abnormal condition of the power supply have become a main research and development focus in the industry.
Refer to FIG. 1 for a circuit block diagram of a conventional power supply that outputs DC power. The power supply is connected to an external power source, and includes a primary rectification and filter circuit, a transformer and a secondary rectification and filter circuit to transform and output a plurality of DC powers to the loads at the rear end. The output DC power has electricity level specifications of 12V, 5V, 3.3V and the like. As the power consumed by the electronic devices of users increases constantly, the conventional technique that adopts a single transformer has to boost power by increasing the coil number and total size. But the dimension and interior of the power supply cannot be changed under the present specification. Hence fabrication of a single transformer is quite difficult. Not only the size cannot meet requirements, voltage transformation generates high temperature which cannot be cooled effectively. As a result, operation of electronic elements is affected. Moreover, the DC power output from a single transformer includes multiple sets of electricity level, a greater power loss incurs.
To remedy the aforesaid disadvantages, there is an approach that adopts multiple transformers to provide DC power output through component voltage. FIGS. 2 and 3 are examples of such a technique. In FIG. 2, one transformer outputs only DC power of 12V, and another transformer outputs DC power of 12V, 5V and 3.3V. Thus the main DC power of 12V adopts the design of dividing current. But for the transformer that outputs multiple sets of DC power, the current passing through is not reduced, and the temperature of the transformer increases significantly. In FIG. 3, the high voltage power and the low voltage powers are controlled respectively by separated transformers. As the DC power of 12V is the main power supply, the temperature of the two transformers differs. Moreover, the total size cannot be reduced. Installation of the power supply is difficult when power requirement increases.